UD Programs Concept 3: Provide physical and

Gummy Capsules
Sodium alginate
(a polymer)
and blue dye
dissolved in water
Calcium chloride
dissolved in water
When the two liquids
combine, they form a
gooey blob (a gel)
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What’s a Polymer?
Polymers are made up of many, many molecules all strung together
to form really long chains.
Polymer chains often get tangled up, like a mound of spaghetti.
http://pslc.ws/macrog/kidsmac/index.htm
http://chemwiki.ucdavis.edu/Wikitexts/Simon_Fraser_Chem1%3A_Lower/States_of_Matter/Polymers_and_Plastics
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What are Hydrogels?
polymer
• Hydrogels are 3-dimensional
polymer networks that are filled
with water
• Contain so much (>90%) water
that they’re kind of like “solid”
water
• Have properties between those
of solids and liquids
water
Schematic of a polymer gel
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How do Gummy Capsules Form?
Add
calcium
ions
Gels form when the polymer
networks are crosslinked
Crosslinks are bonds between
different polymer chains
http://www.intechopen.com/source/html/37702/media/image2_w.jpg
When you drop sodium alginate into
the calcium solution:
• Calcium replaces sodium
• Calcium forms crosslinks
• Why does this change matter? Unlike
Na+ ions, Ca2+ ions can form two bonds
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Spherification vs. Reverse Spherification
Sodium
alginate
Spherification
Drop alginate into calcium chloride
Calcium ions are much
smaller than strands of
sodium alginate, so they can
move (diffuse) much faster
Calcium chloride
Calcium
lactate
Sodium alginate
Why does order matter?
Reverse Spherification
Drop calcium lactate into alginate
Sodium
alginate
Calcium
chloride
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Spherification vs. Reverse Spherification
Sodium
alginate
Calcium chloride
• Calcium moves into the drop, so gelation
occurs inside the sodium alginate drop
• After rinsing, calcium keeps moving
toward the center
• Gummies become more solid over time
Calcium
lactate
Sodium alginate
• Calcium moves into the alginate bath, so
gelation occurs on the outside of the drop
• After rinsing, the reaction stops, since
rinsing removes the un-reacted alginate
• Gummies are stable
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Factors that Affect the Gummies
• Amount of calcium in the alginate solution
• If the sodium alginate solution contains any calcium, gelation (crosslinking) can happen before you drop it into the calcium chloride
• Preventing/fixing this problem:
o If you’re dissolving the sodium alginate in a liquid other than water, make
sure it doesn’t contain calcium (e.g., milk)
• pH of the alginate solution
• If the pH of the sodium alginate solution is too low, the hydrogen
concentration will be too high and alginate won’t react with the calcium
• Preventing/fixing this problem:
o Measure the pH of your sodium alginate solution (shouldn’t be an issue if
you’re just dissolving the sodium alginate in water)
o If the pH is too low, add some sodium citrate
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Another Tasty Hydrogel: Jello!
Cool
[Hot]
[Cold]
Jello/gelatin
• Dissolve gelatin in hot water; let it cool
• As the gelatin solution cools, the
structure changes and crosslinks form
Candy connection: Jello!
http://www.intechopen.com/source/html/17237/media/image13.png
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Capillary Action and Chromatography
Capillary action is the ability of a liquid to
flow in narrow spaces— even against
gravity.
Chromatography is a method for
separating a mixture into different parts.
Some types of chromatography, like paper
chromatography, rely on capillary action.
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Capillary Action in Nature
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Capillary Action
Liquid wets walls
of tube, increasing
surface area.
Surface tension acts
to decrease surface
area, pulling liquid up.
Wetting continues
from a higher level,
causing liquid to
continue rising.
Eventually the liquid
reaches a height at
which its weight is
balanced by surface
tension. After this, the
height stays constant.
For a more thorough discussion of Capillary Action, you can
watch a recording of our brown-bag from March 17, 2014.
http://www.nisenet.org/search/product_category/online-workshops-31
http://chemwiki.ucdavis.edu/Under_Construction/chem1/States_of_Matter/Liquids_and_their_Interfaces
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Paper Chromatography Activity
(1) Draw on paper
(2) Squirt a drop of water onto the paper
(3) Hold the paper vertically
Water and ink move up
the paper, against gravity
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Paper Chromatography
• Water-soluble parts of the ink dissolve
into the water
• Dye moves with the water up the paper,
due to capillary action
• Different dyes travel different amounts
• The distance each dye travels depends
on how the dye dissolves in the water
and how the dye interacts with the paper
Water and ink move up
the paper, against gravity
13
Candy Chromatography
• Dampen candy slightly, then rub
candy onto the filter paper
OR
• Dissolve candy in water, then use a
pipette or popsicle stick to transfer a
small drop onto the filter paper
• Let paper dry
Activity write-ups:
• http://howtosmile.org/record/9665
• http://www.scientificamerican.com/article/bringscience-home-candy-chromatography/
• http://www.sciencebuddies.org/science-fairprojects/project_ideas/FoodSci_p006.shtml
• Then suspend filter paper in a
container of water
• Many people think a 0.1% NaCl
solution works better than pure water
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Will the Colors Separate?
• Most of our foods can only use 7 synthetic colorants
• Brown M&Ms worked the best for me (most separation)
• I didn’t see color separation for orange Skittles or M&Ms;
maybe the dye is just Yellow #6, instead of a combination
of red and yellow dyes
Name
Color
Blue #1
Dark turquoise blue
Blue #2
Dark navy blue
Red #3
Red
Red #40
Dark red
Orange M&M
Blue
Green(?)
Yellow
Red
Yellow
#5
Yellow
Yellow
#6
Dark orange
Green #3
Dark blue-green
Brown M&M
http://www.fda.gov/forindustry/coloradditives/coloradditiveinventories/ucm115641.htm
Green M&M
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Why do the Colors Separate?
Why do some colors move further than others?
Like dissolves like
• Water is polar (charges aren’t distributed evenly)
Red = more negative Blue = more positive
• The most polar dyes dissolve in water the best,
and move the farthest
So if we change the solvent,
colors dissolve differently and
move different amounts
From left: blue, green, red,
yellow
To get more info on this experiment: http://www.rfwp.com/samples/dr-daves-chemistry.pdf#page=4
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Other Chromatography Methods
• Universal goal: for the different parts of a
material to move at different speeds, so they
can be separated and/or analyzed
• One example: HPLC, where a pressurized
liquid moves through a column filled with
silica beads
• Materials can be separated into parts based
on different properties, such as
•
•
•
•
Charge, polarity
Hydrophobicity
Affinity
Size, shape
http://www.saylor.org/site/wp-content/uploads/2012/07/Chapter121.pdf
Liquid
chromatography
system from Agilent
More Resources
•
Descriptions of different spherification ingredients
http://www.molecularrecipes.com/spherification/started-spherification/
•
Good description of science behind spherification
http://itschemicallydelicious.wordpress.com/2013/02/07/the-science-behind-spherification/
•
“What is Jello-O?” (Scientific American)
http://www.scientificamerican.com/article/what-is-jell-o-how-does-i/
•
“What’s that Stuff: Jell-O” (Chemical and Eng.
News)http://pubs.acs.org/cen/whatstuff/stuff/8120jello.html
•
Good discussions of paper chromatography with food dyes (discusses the changes you
get when you dip the paper into water versus other liquids)
http://micro.sci-toys.com/node/45
•
Paper chromatography with markers, using water and alcohol
http://www.kyantec.com/Tips/paperchromatography.htm
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